1. Field of the Invention
This invention relates to the attenuation of aircraft jet engine sound frequencies and more particularly to a bullnose fairing assembly for installation in an aircraft thrust reverser.
2. Description of the Related Art
Aircraft engine noise is a significant problem in high population areas and other noise controlled environments. To mitigate this problem efforts have focused on lining the aircraft nacelle and surrounding engine areas with acoustic liners to reduce the amount of noise radiating to the community.
U.S. Pat. No. 4,421,201, issued to M. D. Nelson et al, discloses a broadband acoustic resonator and absorption panel used for reducing engine noise from high bypass fan jet engines mounted on an aircraft.
U.S. Pat. No. 5,782,082, issued to Hogeboom et al, discloses an aircraft engine acoustic liner for use in dissipating low mode order noise. The low resistance liner includes a middle layer, having partitioned cavities. The cavities aid in scattering a large amount of low mode order noise into higher mode order noise. An imperforate sheet is attached to one side of the middle layer. A perforate sheet having a large open surface area is optionally attached to the middle layer. The perforate sheet stops the whistling effect caused by high speed air flowing into the cavities and minimizes airflow drag.
U.S. Pat. No. 4,122,672, issued to Lowrie et al, discloses an acoustic liner that forms part of the fan duct wall near the blade tips and combats the degeneration by reinforcing the regular shockwave pattern at the expense of the irregular one. This is achieved by making the cells equal to half the wavelength of the blade passing frequency at the predetermined supersonic condition of interest.
U.S. Pat. No. 5,975,237, issued to Welch et al discloses a reinforcing structure for an engine nacelle acoustic panel that is used for a thrust reverser panel. However, the bullnose fairing is not acoustically protected.
None of the aforementioned references address the acoustic treatment of a bullnose fairing of a thrust reverser.
The present invention is an acoustically treated bullnose fairing assembly for a thrust reverser of an aircraft, the thrust reverser having an outer fixed structure and a stowable blocker door. The bullnose fairing assembly includes a back sheet, a face sheet and a honeycomb structure positioned between the face sheet and the back sheetxe2x80x94these three items being bonded together and securely affixed to an outer fixed structure of the thrust reverser. The back sheet has a forward end and a back end. The face sheet has a forward portion and a back portion, the back portion being aft of a forward edge of the blocker door when the blocker door is stowed. The forward portion of the face sheet is perforated. The perforated forward portion of the face sheet cooperates with the honeycomb structure to maximize the acoustic performance of the thrust reverser. This added acoustic capability provided to the treated bullnose fairing assembly can increase the total acoustic area of the thrust reverser by approximately 5 percent, depending on the diameter and length of the thrust reverser.
The back sheet is preferably affixed to the thrust reverser by a set of forward fastening elements that fasten the backsheet to a forward portion of an outer fixed structure of the thrust reverser. The forward fastening elements are blind fasteners that do not extend through the bullnose fairing assembly to the face sheet.